In making a diagnosis of arterial sclerosis, the intima-media thickness (which will be abbreviated herein as “IMT”) of a carotid artery is known as one of most important indices to the status of an initial atherosclerotic. The “IMT” refers to the thickness of a complex of the intima and the media of a vascular wall of a carotid artery. In FIG. 16, the IMT refers to the thickness of a layer (i.e., an intima-media 24) that is seen between the lumen 23 and adventitia 25 of a blood vessel.
The IMT is generally obtained by detecting the boundary between the lumen 23 and intima of the blood vessel (which will be referred to herein as a “lumen-intima boundary 26”) and the boundary between the media and the adventitia 25 (which will be referred to herein as a “media-adventitia boundary 27”) and measuring the distance between these two boundaries using an ultrasonic diagnostic apparatus. For example, Patent Documents Nos. 1 and 2 disclose an ultrasonic diagnostic apparatus which measures the IMT automatically.
In measuring the IMT, ordinarily a predetermined IMT measuring range 30 is set in the long-axis direction of the carotid artery 20 (i.e., the direction in which the blood vessel extends) as shown in FIG. 16 and either the maximum thickness (max IMT) or average thickness (mean IMT) of the IMTs measured in the IMT measuring range 30 is regarded as an IMT value. For example, Non-Patent Document No. 1 recommends that the IMT measuring range 30 be set at 1 cm away from the far end (i.e., closer to the head) of the common carotid artery (CCA) of the carotid artery 20.